Most of finite linear motion guide units of the sort recited just above conventionally have a pair of elongated guideway members moveable relatively to each other, and a cage or retainer lying between the guideway members to space the rollers as rolling element from each other. The cage or retainer is constituted with a retainer plate which is set to travel over a distance of stroke half the relatively moving stroke of the guideway members. With the finite linear motion guide units constructed as stated earlier, however, the cage or retainer is likely to be off or stray in increments out of a desired location it should be relative to guideway members because of different working conditions including variations in load carried on the finite linear motion guide unit, machining accuracy of raceway grooves made on the guideway members, working geometry where the guide unit operates in an upright posture, high traveling velocity, high acceleration/deceleration, and so on. To cope with the issue stated earlier, most of the finite linear motion guide units have conventionally the cage with means for keeping the cage against straying from the desired location. A common example of the prior means for preventing the cage from straying installed in the finite linear motion guide units is composed of a rack-and-pinion mechanism in which the cage has a pinion while the guideway members have racks, respectively, so that the pinion comes into mesh with the racks to correct for the relative location of the cage to the guideway members, keeping the cage in place with respect to the guideway members.
In the commonly-assigned Japanese Laid-Open Patent Application No. 2003-176 820A, now matured into JP patent No. 3 950 683,there is disclosed a finite linear motion guide unit having a rack-and-pinion mechanism to keep the cage in place with respect to the guideway members. With the prior finite linear motion guide unit, the smaller pitch or distance between the center-lines of adjacent rollers for rolling elements that are installed in a cage or retainer results in the greater number of the rollers lying in a preselected length of the cage to get an effective raceway area where a raceway groove comes into rolling contact with the roller as wide as possible to thereby enhance the load-carrying capacity. Moreover, the raceway groove of V-shaped in transverse section is cut larger in depth as well as in width than ever to make larger the effective width of raceway surface across which the raceway surfaces of the guideway members come into rolling-contact with the rollers, making certain of the heavier load-carrying capacity. In the prior finite linear motion guide unit, moreover, there is provided a pinion-holder arrangement composed of a pinion holder and a pinion received inside the holder for revolution. The pinion-holder arrangement is installed in the cage or retainer to get the pinion coming into mesh with racks lying on the guideway members, thereby making sure of the linear motion of the guideway members relative to each other without causing displacement of the cage out of a desired relative location to the guideway members even under higher acceleration/deceleration. There is disclosed a rack composed of teeth spaced apart from one another at preselected intervals to mesh with the teeth on the pinion, and side walls extending lengthwise of the rack with flanking sidewise opposite ends of the teeth to connect the successive teeth with each other. The lengthwise sidewalls of the rack are thick sidewise to splay out with depth to come into face-to-face engagement with their associated inside surfaces of a gutter deep in the guideway member when the rack fits in the gutter, thereby helping keep securely the rack in the gutter of the guideway member.
Another commonly-assigned Japanese Laid-Open Patent Application No. 2007-232 061 discloses a finite linear motion guide unit having a rack-and-pinion mechanism in which a pinion holder is composed of a pair of pinion holder halves, which are fastened together in a snap-fit joining manner to render the pinion holder with tiny construction increased in mechanical strength to the extent making it possible to utilize the pinion holder in large machines. The means for keeping the cage in place relatively to the guideway members in the prior finite linear motion guide unit recited just earlier is comprised of a pinion holder fitting into a window cut in the cage, racks lying on sides of the guideway members, one to each side, and a pinion provided with teeth mating with the racks and installed in the cage for rotation. The pinion holder is made up of holder halves, any one of which lies on any one side of the cage along a marginal edge of the cage at the same marginal edge of the window. The holder halves have sidewise extensions or flanges to firmly squeeze the cage between them along the marginal edge of the window.
With the finite linear motion guide unit disclosed in the prior art recited the second patent literature, nevertheless, the cylindrical rollers for rolling elements are retained in the cage by means of fingers which need a space larger than a thickness of the cage to bear any one of axially opposite ends of the roller. As a result, the finger construction as stated earlier is inevitably hard to makes the effective raceway area where a raceway groove comes into rolling contact with the roller as wide as possible to increase the load-carrying capacity. Moreover, when making the raceway grooves in the guideway members larger in depth while rendering the cage plate as less as possible in thickness to ensure the effective raceway area wider than ever, there can be provided no construction to retain the rollers on the edges around the openings to receive the rollers therein. As a result of no construction to retain the rollers, the rollers might be more likely to easily fall away from the cage on assembling phase of the finite linear motion guide unit.
Meanwhile, modern industries are in need of the finite linear motion guide unit more in load-carrying capacity than ever as well as capable of operating under working conditions which expect the guideway members to travel or move past relatively each other with higher acceleration/deceleration. With the prior finite linear motion guide unit, a cage plate 46 for a cage or retainer 45 constructed as shown, for example, in FIG. 18 is made therein with a series of elliptical openings 47 to receive therein the rollers. Nevertheless, there is provided no means such as fingers and so on to retain the rollers in the cage. This means the cage plate 46 in itself and of itself couldn't retain or keep the rollers in place.